Biosensor arrays are used to detect molecules in an analyte that is to be tested. Arrays of this type are increasingly realized on chips, with a view to miniaturization. The sensors are often arranged in large numbers on a substrate. The high degree of parallelism allows different tests to be carried out in parallel at the same time, for example tests for the presence of different substances (e.g. molecules) in a predetermined analyte. This property indicates that sensor arrangements of this type, including a corresponding evaluation system, have numerous possible applications in medical diagnostics, such as for example in the point-of-care or home-care sector, in the pharmaceutical industry (e.g. for pharmaceutical screening, pharmacogenomics, high throughput screening HTS)), in the chemical industry, in food analysis, in general scientific research, such as for example gene sequencing, and in environmental and food technology.
To functionalize such biosensors or biochips, it is customary for a small quantity of binding-ready capture molecules, also referred to as probes, for example a specific nucleic acid sequence, to be immobilized on the surface of a specifically configured substrate (biochip base module). This immobilization, according to the coupling chemistry used, is usually implemented at the substrate surface in such a manner that the capture molecules remain thereon even in the event of washing processes. Therefore, the basic principle of many known sensors is based on first of all capture molecules of this type being applied to a chip in a position-specific manner, for example using micro-dispensing techniques, and being immobilized using a corresponding binding chemistry. The application is preferably in an array format, in which case, by way of example, different oligonucleotide sequences can be immobilized at different array positions.
By minimizing the dimensions of the individual positions of an array, it is possible on the one hand to increase the array density and on the other hand to improve the sensitivity of detection. Then, by way of example, highly parallel DNA analyses can be carried out by means of a DNA microarray formed in this way. The analyte molecules to be tested, such as for example nucleic acids, are usually marked and hybridized with the capture molecules such as for example nucleic acids, on the chip. Hybridization generally takes place only between exactly complementary nucleic acid molecules. The intensity of the signal measured is usually proportional to the quantity of hybridized sample.
The abovementioned arrays have in recent years also been realized on an industrial scale in a biochip with integrated electronic evaluation technology. A biochip of this type allows fast, simple and inexpensive analysis of biomolecules, such as for example the abovementioned nucleic acids or proteins, in clinical diagnostics and patient-individual medicine. A biochip of this type or its base module may, for example, contain a multiplicity of miniaturized sample holders or sensor elements with metal electrodes, such as for example gold electrodes, which are arranged in an interdigital structure and to which biomolecules can in each case be applied. The evaluation is then effected using extremely small current profiles. Biochips of this type are based on a standard CMOS (Complementary Metal Oxide Semiconductor) semiconductor fabrication process with additional gold electrodes.
However, one drawback of the fabrication of biosensors of this type is that to date functionalization of semiconductor chips, for example with organic molecules, such as DNA or proteins, has not been possible at wafer level, since the functional layer, i.e. the layer which comprises the capture molecules, cannot be preserved for a prolonged period of time and is often destroyed during singulation, i.e. when the chips are being sawn out. Moreover, the application of a defined quantity of functional molecules for functionalizing the sensor fields is problematic, in that divergent flow on the part of the liquid quantity reduces the concentration, and if the liquid quantities flow into one another sensor signal crosstalk occurs.
A further drawback is that a complex but ultimately inadequate cleaning procedure has to be carried out prior to the functionalization. Another problem of the biosensors available in the prior art is the occurrence of offset currents, caused by unspecific reactions, during electrochemical reading.
To overcome the abovementioned problems, at present, after singulation, the chips are cleaned and functionalized individually by hand, which is expensive. However, such handling cannot be implemented on a large industrial scale.